Some vehicle engine systems utilizing direct in-cylinder injection of fuel include a fuel delivery system that has multiple fuel pumps for providing suitable fuel pressure to fuel injectors. This type of fuel system, Gasoline Direct Injection (GDI), is used to increase the power efficiency and range over which the fuel can be delivered to the cylinder. GDI fuel injectors may require high pressure fuel for injection to create enhanced atomization for more efficient combustion. As one example, a G DI system can utilize an electrically driven lower pressure pump (i.e., a fuel lift pump) and a mechanically driven higher pressure pump (i.e., a direct injection pump) arranged respectively in series between the fuel tank and the fuel injectors along a fuel passage. In many GDI applications, the lift fuel pump initially pressurizes fuel from the fuel tank to a fuel passage coupling the lift fuel pump and direct injection fuel pump, and the high-pressure or direct injection fuel pump may be used to further increase the pressure of fuel delivered to the fuel injectors. Various control strategies exist for operating the higher and lower pressure pumps to ensure efficient fuel system and engine operation.
In one example approach, as shown by Ulrey and Pursifull in US 2016/0025030, voltage (and current) is provided to a lift fuel pump in a continuous or a pulsed manner based on a number of parameters, such as engine speed and load, and an amount of fuel to be supplied to the engine. By switching between the two modes, fuel economy is improved via pulsed lift pump operation while presence of fuel vapor at the high pressure pump inlet is avoided.
However, the inventors herein have recognized that the switching between the modes may make it difficult to self-calibrate the fuel pump controller. Typically, in feedback systems, such as the fuel systems described above, the open loop performance of the fuel system may be characterized while in steady-state (i.e. continuously powered). Centrifugal fuel pumps driven by electric motors have a pressure versus flow characteristic for any given voltage. Since in automotive applications fuel lift pumps rarely operate at the high end of the flow range (such as at 20 ml/s), lift pumps are typically calibrated by characterizing pump pressure as a function of voltage at the lower end of the flow range (such as at flow rates below 2 ml/s). An engine controller may control pump operation to a constant pressure and monitor the voltage, or control to a constant voltage and monitor the pressure. In this way, an in-tank fuel lift pump can be characterized while operating in a steady-state (i.e., the continuously powered mode). However, when in the pulsed mode, since the pump does not reach a steady-state, it may not be possible to characterize the pump. Pump variation over time comes from, the pump's resistance due to filming or a pump winding's thermal conductivity (at the current temperature) may influence the pump characterization. Pump components, such as the filming of a brush/commutator interface and a pump chamber, may wear over time due to abrasive particles moving through the pump chamber. This is particularly exacerbated when the abrasive particles are allowed to recirculate through the pump without filtering. If a pump is not characterized properly, pressure control and thus fueling accuracy may be affected.
In one example, the issues described above may be addressed by a method for a fuel system comprising: operating a lift fuel pump in a pulsed energy mode including ramping up the voltage (or current, or power, or speed) during the pulsed mode; and calibrating the lift pump based on a ramp rate during the pulses relative to a rate of change of the estimated fuel pressure. In this way, a lift pump may be characterized even while it is operated in a pulsed mode.
As one example, during operation of a fuel lift pump in a pulsed mode, the duty cycle pulse applied to an electric (DC) motor of the lift pump may be gradually ramped up. (The pump is typically controlled by a duty cycled voltage at a frequency of 10 kHz (for example). This short electrical pulses occurring each 0.0001 seconds are not the ones of which we speak. These fast occurring pulses for an effective applied voltage to the pump motor. The pulses of which we speak are the effective voltage that may be applied for 0.25 seconds to restore pressure and then shut off for 8 to 0.5 seconds until the pressure again requires restoration. Within that 0.1 to 0.4 second voltage pulse, this may include a ramping up of the applied voltage, or alternatively, of the applied power, current, or pump speed. In one example, the rate of ramping up the pump pulse may be based on a ramp speed which yields maximum electrical savings. Alternatively, the pressure rate might be further limited to limit the pressure rate of change during a scheduled injection. At the same time, the resulting fuel pressure rise rate (that is, a derivative indicative of the rate of rise in fuel pressure) may be estimated. The fuel pump is then characterized based on the ramp rate of the applied voltage ramp (during the pulse) relative to the rate of fuel pressure change. In one example, a pump gain factor is determined based on a ratio of the applied pulse and the measured rate of pressure rise. During subsequent fueling, pump operation is adjusted as a function of the newly learned gain factor.
In this way, a fuel lift pump may be operated in a pulsed mode to reduce energy consumption while providing robust characterization of the lift pump. The technical effect of applying a ramped pulse is that a change in the applied pulse (e.g., voltage or current or speed) can be better correlated with a resulting change in fuel pressure. This may allow for a better calibration of the fuel pump. This online calibration compensates for changes over manufacture or time such as brush/commutator filming, motor temperature, and pump chamber wear. By calibrating the pump reliably and accurately, fuel pressure control performance and thus overall engine fuel economy is improved. By calibrating the pump without interrupting the pulse mode of lift pump operation, the pulsed mode can be extended over a longer portion of a drive cycle, improving the associated fuel economy benefits.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.